1. Field of the Invention
This invention relates to a radial flow water filter having a casing defining an upright, annular in cross-section chamber. The filter has an air distributor for fluidizing filter media particles within the chamber during introduction of backwash fluid, the latter of which flows radially along a path at an angle to the fluidized motion of the particles.
2. Description of the Prior Art
Separation of solids from liquids is commonly achieved by utilization of a filter having a filtration media comprised of discrete particles. Oftentimes, filtration is accomplished by downflow or gravitational movement of contaminated water through a horizontal, rectangular bed of sand supported by a bed of gravel. As the water moves through the voids in the filter, separation of solids occurs due the mechanisms of straining, flocculation and/or sedimentation.
Conventional downflow filters make effective use of only the top few inches of the bed, even though the latter may be two feet or more in depth. After a period of time (which is dependent upon the incoming rate of solids), the filter becomes plugged to a degree such that an excessive resistance to the incoming flow of water is presented. At this time, the flow of influent water is interrupted, whereupon the bed is taken out of service for cleansing.
Typically, particulate media filters are cleaned by a process known as backwashing, wherein a large quantity of water is directed through the filter in reverse flow direction to flush off the suspended solids that have accumulated in the voids between the sand. The clean backwash water, which often is previously treated water held in storage, is directed up through the filter bed, and the water along with the flushed solids flow over the top of the bed and toward a second storage receptacle. Subsequently, the used backwashing water must be sent back to the treatment plant for reprocessing.
As should be obvious, it is desirable to reduce the quantity of backwash water that is required to properly cleanse the filter, as well as the amount of time that the filter is out of service for backwashing. The volume of the storage tanks required for backwasing is directly related to the volume of water required for backwash. Moreover, flow of used backwash water back to the plant for reprocessing reduces the amount of incoming contaminated water that the plant could otherwise treat, such that the overall capacity of the plant is correspondingly reduced.
In particular, the backwashing operation is particularly critical in waste water treatment plants. Oftentimes, the backwashing fluid directed back to the plant for reprocessing creates a hydraulic overload, which upsets the plant and results in additional solids being directed toward the filter. Consequently, backwashing must occur at more frequent intervals, proportionately raising the amount of water necessary for reprocessing. A cycle thus begins that can disastrously result in plant failure and consequential pollution of the receiving stream.
In the past, various attempts have been made in an effort to reduce the quantities of water required for proper backwashing as well as the amount of time that the filter is out of service. In some instances, pressurized air is introduced through a plurality of nozzles disposed at the horizontal bottom surface of a conventional rectangular sand filter, such that the air agitates the surrounding said particles as well as the filtered solids. However, it has been found that such a filter bed cannot be maintained in a state of fluidization by the air during backwashing, since the agitation often causes the sand to flow over the top of the filter bed along with the backwashing water.
As can be appreciated, it would be a desirable advance in the art if means were provided to efficiently cleanse a filter using a minimum quantity of backwash water as well as a minimum amount of time that the filter is out of service.